There are a number of medical devices used to create void spaces such as cavities or channels in living tissue such as bone. One such device is a cavity creator. A cavity creator is a surgical tool assembly that, as implied by its name, forms a cavity in the tissue of a living being. A number of cavity creators are specifically designed to form cavities in hard tissue, more specifically, bone. This type of cavity creator may be used in a procedure generally known as a vertebral augmentation procedure. In a vertebral augmentation procedure, cement is injected into a vertebral body that is suffering from fracture so as to stabilize the vertebral body. It is believed that this stabilization reduces the pain the fracture would otherwise induce in the patient. As part of this procedure, to ensure a sufficient quantity of cement is introduced into the vertebra, it may be necessary to form a cavity, sometimes referred to as a void space, in the vertebra.
A cavity creator that forms a void space in a vertebra typically includes two components, an access cannula and a curette. The access cannula is a tube like device. The access cannula is inserted in the patient and into the vertebra to be filled with cement. The curette includes an elongated shaft dimensioned to extend through the lumen, the bore, of the access cannula. A tip is located at the distal end of the shaft. A handle is located at the proximal end of the shaft. Once the curette is seated in the access cannula the tip is positioned to extend radially, outwardly from the longitudinal axis of the access cannula. The rotation of the curette results in the pressing of the tip against the bone located outwardly from the access cannula. The pressing of the tip against the bone abrades the bone so as to form a cavity, the void space, internal to the vertebra that extends radially beyond the access cannula. Once this cavity is formed, the curette is withdrawn. Cement or other therapeutic agent is then introduced into the bone and more particularly the cavity that surrounds the open distal end of the access cannula.
Some curettes include a tip that is pivotally attached to the distal end of the curette rod. A drive shaft internal to the rod is selectively extended/retracted to pivot the tip between an orientation in which the tip is axially aligned with the shaft and orientation in which the tip is directed away from the shaft. Some of these curettes rely on a thumb wheel and gear assembly mounted to the curette handle to selectively extend/retract the drive shaft. Still other of these curettes include ratchet mechanisms again mounted to the handle, to extend/retract the drive shaft.
A disadvantage of a number of these curettes is that their internal components do not allow one to easily set the extended state position of their drive rods. This means that, in turn, it is difficult to set this type of curettes so as to with a degree of precision, control the extent to which the tip extends beyond the complementary access cannula. Further some of these curettes include numerous parts. As with any device, the more parts required to build the device increases the cost of providing the device.
Still another known curette includes a shaft with a tip that is formed integrally with and extends distally from the shaft. At least the connector that holds the tip to the shaft is formed from a superelastic shape memory material. This curette is initially seated in the access cannula so that connector and the tip are wholly disposed in the cannula. When the cavity creator is in this state, the connector is bent to generally conform to the shape of the access cannula. The shaft of the curette is extended to cause the tip and connector to extend forward from the access cannula. As the connector emerges from the constraining space of the access cannula, the potential energy of the connector is released. This causes the connector to return to its unconstrained, bent, state. By extension, this results in the movement of the tip radially away from the access cannula. Once the tip is in the desired position, the curette is rotated so as to press the tip against the adjacent bone.
The above-described curette includes a control knob for selectively extending/retracting the shaft. This knob, when rotated, moves towards and away from the curette. The practitioner then has to adjust his/her hand position relative to the handle in order to set the position of the tip. Having to take this extra step adds to the ergonomic complexity of using this type of curette.
Moreover, as a consequence of the rotation of the knob to extend the above-described curette, the overall proximal-to-distal length of this device increases. Often a fluoroscope is in close proximity to the cavity creator when this procedure is performed. The fluoroscope provides real time images of the bone in which the void space is being formed. The increasing length of the handle of this curette can make it difficult to position the curette around the fluoroscope.
Further, many curettes, regardless of the type of assemblies that pivot their tips, share a common problem. When the cavity creator with which one of these curettes is integral is in certain positions, it is difficult for the practitioner to hold the handle so as to rotate the handle and/or set the extent to which the curette shaft is extended. For example, there are times when the practitioner forms a void space that is centered on an axis that extends into the patient through a portal located on the side of the patient opposite the side of the patient against which the practitioner is standing. This is known as the contra-lateral side of the patient. Thus, if the practitioner is standing adjacent the left side of the patient, it may be desirable to create a cavity that is located in bone best accessed from the right side of the patient. The presence of equipment, for example a fluoroscope, may make it difficult for the practitioner to simply reposition himself/herself adjacent the right side of the patient. In this situation, to form the cavity, the practitioner has to reach across the spine of the patient in order to insert the access cannula. When the curette is inserted into the access cannula, the handle does not simply face away from the practitioner as the handle would if located between the practitioner and the patient. Instead, the handle of the curette can be both spaced away from the practitioner and be directed towards the practitioner. To set the extended state position of the curette shaft or rod, the practitioner has to reach across the patient. This puts the hand of the practitioner in an awkward position relative to the component of the curette he/she needs to manipulate. This makes it difficult for the practitioner to set the curette to ensure that tip is properly positioned.
Furthermore, it should be understood that the creation of a void space involves more than simply extending and retracting the shaft integral with the curette. It is also necessary to rotate the curette to press the tip against the tissue to be removed. This means that the practitioner may be required to place his/her hands and fingers in an unusual position in order to both set the extension of the curette and rotate the curette.
Still another class of device used to form a void space in bone are channel creators. A channel creator is typically used to form an elongated bore, a channel, in the bone to which the channel creator is applied. These channels are typically smaller in cross sectional width and often longer in length than the cavities created by a cavity creator. The control members associated with a number of these devices have share a disadvantage with the cavity creators. It can be difficult to control the device depending on the orientation and position of the device relative to the practitioner.